VMWare Configuration Management

I am new to ITIL and currently researching configuration management best practices, and have a few questions:

1) I am aware you should establish "relationships" between CI's to assist in reviewing change control impacts, dependancies, and resolving incidents etc, I was just wondering if any IT departments who follow ITIL and a formal configuration management policy, can you provide a few examples of "relationships" you have defined in your CMDB between the various elements that make up your VMware infrastructure?

2) Common sense suggests it is crucial to ensure all your servers/infrastructure are logged as CI's in your CMDB, as otherwise you cannot tie changes/incidents/relationships to them - but is there any risk in keeping old decommissioned CI's in your CMDB - i.e. say for example an old decomissioned file server which is still showing as deployed in your CMDB - are there any risks in this?